Changing pertussis epidemiology: everything old is new again.

Before vaccination, pertussis was a universal disease of early childhood. Although apparent control of the disease in the United States and other countries was achieved through vaccination, pertussis is resurgent. Though acellular vaccines have been in use for 20 years, new data are emerging on their effectiveness and durability of protection and the contribution of these characteristics to the resurgence of pertussis.